Achieving optimal rheological behavior in cement slurries is imperative to use of cement for drilling and/or cementing. An effective cement system provides isolation between subterranean zones. To effectively utilize cement in a well operation, the cement slurry, upon mixing with water and necessary additives, fillers, etc., must exhibit fluid behavior that allows it to be pumped efficiently downhole without hardening, settling, or damaging equipment and be placed in the desired location where it will set into a hardened material.
Treatment fluids can be used in a variety of subterranean operations. Such subterranean operations can include, without limitation, drilling operations, stimulation operations, production operations, remediation operations, sand control treatments and the like. As used herein, the terms “treat,” “treatment,” “treating” and other variants thereof refer to any subterranean operation that uses a fluid in conjunction with achieving a desired function and/or for a desired purpose. Use of these terms does not imply any particular action by the treatment fluid or a component thereof unless expressly described as such herein. Illustrative treatment operations can include, for example, fracturing operations, gravel packing operations, acidizing treatments, scale dissolution and removal operations, consolidation operations, conformance control operations, and the like.
When performing a subterranean treatment operation, including those noted above, it can sometimes be desirable to temporarily or permanently block or divert the flow of a fluid within at least a portion of the subterranean formation by forming a fluid seal therein. The formation of a fluid seal can itself be considered a treatment operation. Whether the fluid seal is intended to be temporary or permanent can determine the type of agent used in its formation. Illustrative fluid blocking and diversion operations can include, without limitation, fluid loss control operations, kill operations, conformance control operations, and the like. The fluid that is being blocked or diverted can be a formation fluid that is natively present in the subterranean formation, such as petroleum, gas, or water. In other cases, the fluid that is being blocked or diverted can be a treatment fluid, including the types mentioned above. In some cases, treatment fluids can be formulated to be self-diverting, such that they are automatically directed to a desired location within the subterranean formation.
Providing effective fluid loss control during subterranean treatment operations can be highly desirable. The term “fluid loss,” as used herein, refers to the undesired migration or loss of fluids into a subterranean formation and/or a particulate pack. Fluid loss can be problematic in a number of subterranean operations including, for example, drilling operations, fracturing operations, acidizing operations, gravel-packing operations, workover operations, chemical treatment operations, wellbore clean-out operations, and the like. In fracturing operations, for example, fluid loss into the formation matrix can sometimes result in incomplete fracture propagation. Formation of a fluid seal in such treatment operations can mitigate the migration of a fluid into an unwanted location of the subterranean formation.
Likewise, in the reverse of a fluid loss event, incomplete fluid blocking can result in production of an unwanted fluid from one or more zones of a subterranean formation. For example, incomplete formation of a fluid seal may result in the unwanted incursion of formation water or brine into a wellbore, which may decrease the value of a hydrocarbon resource produced therefrom.
Certain non-hydraulic cements (e.g., Sorel cements) may be designed to remain as a low viscosity fluid during placement. The cement slurry may then sets rapidly at a given formation temperature. The transition from fluid state to solid state may be almost immediate, resulting in essentially zero gas migration or channeling. This “right angle set” occurs because the setting process is highly exothermic. Due to low viscosity, however, the fluid may have a tendency to flow to the low side in a horizontal well. This may result in incomplete sealing of high side of the horizontal well allowing for undesired fluids flow into the well through the unsealed portions. It is important that, once placed, the fluid retain its shape without flowing to lower side of the wellbore. The fluid preferably seals the zone uniformly upon hardening. This will require the fluid possess shear thinning or pseudoplastic rheological properties to prevent slumping. Even though viscosifiers such as xanthan have been used to prevent particle settling of insoluble components (magnesium oxide) of the fluid, the rheology of the resulting viscous fluid may not prevent slumping of the fluid in a horizontal well.